1. Field of the Invention
The present invention generally relates to technology for changing a shift characteristic of an automatic transmission connected to an engine to transmit power from the engine. More specifically, the present invention relates to changing of the shift characteristic of an automatic transmission to enable the rotational speed of the engine to be limited to an upper limit value in a satisfactory manner when the upper limit value is being limited to a lower rotational speed due to such circumstances as execution of an engine protection control, the engine system being cold, or execution of a failsafe control.
2. Background Information
Many vehicles are provided with a shift control apparatus to control shifting of an automatic transmission connected to an engine to transmit power from the engine. One example of shift control apparatus is disclosed in Japanese Laid-Open Patent Publication No. 11-48830, which discloses limiting an upper limit value of the engine rotational speed to a lower engine rotational speed limit than normal and changing a shift characteristic of a shift schedule of the automatic transmission in a direction of a lower vehicle speed.
In Japanese Laid-Open Patent Publication No. 11-48830, the engine control apparatus and the shift control apparatus cooperate together when an upper limit value of the engine rotational speed is being limited to a lower rotational speed due to certain circumstances occurring. In particular the engine control apparatus reduces an overlap angle of a variable valve system of the engine and lowers a maximum rotational speed limit of the engine, i.e., lowers a red zone, allowable rotational speed, or rotational speed upper limit value of the engine. Simultaneously, the shift control apparatus changes a shift characteristic curve of a shift schedule of the automatic transmission toward a lower vehicle speed such that the automatic transmission tends to upshift, i.e., such that a higher gear stage or lower gear ratio is selected than under normal circumstances in which the maximum rotational speed limit is not lowered. As a result, the engine rotational speed decreases when the automatic transmission is in a higher gear stage or lower gear ratio.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved shift control apparatus. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.